Dibasic acid manufacture



April 4, 1961 H. cHAFE-rz ErAL 2,978,473

DIBAsIc ACID MANUFACTURE emglled sept. so, 1958 z l I f nitedA StatesFishkill, N.Y., assignors to Texaco Inc., a corporation of DelawareFiled Sept. 30, 1958, Ser. No. 764,324

'12 Claims. (Cl. 260-452) This invention relates to a process forproducing dibasic acids and more particularly to a process for theirproduction from paratlinic hydrocarbons having a boiling point above 100F. such as paraiiin Wax, slack wax and parailinic lube oils.

The dibasic acids and their derivatives, e.g., succinic, glutaric,adipic, pimelic and higher acids are useful in the manufacture of oiladditives, plastics, plasticizers, pharmaceuticals'and syntheticlubricants. Esters of the higher molecular weight dibasic acids (C6-Hare particularly valuable as synthetic lubricants because of their lowpour point and high viscosity index. The dibasic acids and theiranhydrides are useful for the manufacture of alkyd resins withpolyhydric alcohols. The acids may be converted also in a conventionalmanner to amides, metal soaps and the like.

In Vthe oxidation of saturated aliphatic hydrocarbons, it has been knownto employ nitric acid as the oxidizer. While the dibasic acids producedfrom such a process are satisfactory, the amount of nitric acid requiredper part dibasic acid producedY is generally so large as to make theprocess commercially unattractive.

In the prior art there was developed a method of more effectivelyutilizing nitric acid in dibasic acid manufacture by iirst oxidizingAaliphatic hydrocarbons with air in the presence of catalyst, subjectingthe air oxidate to atet extraction with an alkanol ora dialkyl ketoneextractant or selective solvent, stripping off ltheextractant andoxidizing the extraction residue with high strength nitric acid of aconcentration above about `50%, preferably 70%. VAlthough this methodsignificantly reduces the consumption of nitric acid perpart of dibasicacid producedit has the major disadvantage of requiring `the utilizationof nitric acid having a concentration of at least. 50% in order toobtain areasonably low` nitric acid consumption. Such high strengthnitric acid has the greater disadvantage of being able to trigger and`sustain explosions. ln additiomrhigh strength nitric acid is dilicnltto control lreactionwise Vand is highly corrosive to reaction apparatus.Besides `the disadvantage of Vemploying high strengthl acid, the priorart method requires the stripping olf of the alkanol or ketone selectivesolvent prior to nitric acid oxidation. Such a stripping operationsubstantially adds `to the cost of production.

As an improvement oVerthe prior art, we have devised a novel method ofproducing dibasic acids whereby the stripping olf of the extractant isnot required, prior to nitric acid oxidation; and whereby dilute nitricacid (less than about 40%) renders a better utilization of the nitricacid values than the concentrated acid (greater than about50%); andwhereby the more dilute the nitric acid the lower the acid consumptionper part dibasic acid produced.

Broadly, our process for the production of dibasic acids. comprisessubjecting a parainic, oxidate to water extraction, separating theaqueous phase from the oily rafnate, reacting the aqueous phase withVdilute nitric acid thereby 4further oxidizing the Watersoluble parainicoxidates to dibasic acids, and recovering the dibasic acids from theaqueous phase.

This process lis a low cost, rapid and eflicient method' for obtainingdibasic acids. In addition, it yutilizes nitric acid to a degree ofeiiciency and economy unknown before in the prior art.

FIRST STAGE-OXIDATION WTH OXYGEN In the first stage of our process, theoxidizing medium employed is elemental oxygen either in pure form orV ina mixture of other gases, e.g., air. It is of paramount importance thatthe gas oxidation be carried on in -a manner to obtain an oxidateproduct having a saponication number of at least 200, advantageously 300to 600, and preferably between 400 and 600. Before the water extractionand nitric acid oxidation steps, saponication number is determined bythe procedure set forth in ASTM Method of Test, D94-56T. Thiscontrol'con- Vtributes in part to the high yield of dibasic acids ob- Y-tained and the ease of purifying the final dibasic acid product. Theease of puriiication is perhaps due to the vstripping out of light endssuch as low molecular Weight monobasic acids, etc., byextensive gasoxidation prior to .the water extraction and nitric acid treatment.`

A preferred charge Ifor the initial molecular .oxygen oxidation(preparatory to Water extraction) is macrocrystalline parain wax.Macrocrystalline paraffin wax is predominantly a straight chainsaturated hydrocarbon lhaving from 18 to 32 carbone atoms per molecule.`Good dibasic acids were obtained withV a semi-rened deoiled paraliin waxcontaining. as d n little as 0.5% oil, a crude. scale wax containingsomey what under 5 oil and wax concentrate having between.

yields of whiteL crystallineV about 5 and 40% Voil content. The latterWax, a relatively high oil content wax, is termed slack wax in thetrade. Y

The primary oxidation is conducted in any. conventional mannerpermitting attainment of the necessary high saponication number.Suitable oxidation of yslack wax for use. in our process can be doneinaccordance with the procedure described in U.S. Patent No. 2,8475 f439. The less oily Wax, such as deoiled paratiin wax,

obtained by solvent dewaxing a distillate oil, pressing and sweatinga'distillate oil, or` a combination processy of extractive solvent.Irening, canv be oxidized to the,...

needed high vsaponiiication number with an oxygen-containing gasaccording to the process disclosed inlco-f v pending, co-assignedapplication, Serial No. 492,746, filed' l yMarch 7, 1955, now U.S.Patent No. 2,862,803(

Highly oxidized wax oxidates produced from'rparan. Y, i wax :containingless than 5% oil'by use of* thelattenl process to f obtainneutralization-saponiiication numberV ratios above `about 0.6y are apreferred oxidategc'harge'.` K stock for use in our invention. 'Inf suchoperations fthe'.v deoiled paraiin Wax is reacted with air with oryWithout the presence yof a metalliferous catalyst at a tcmperaturerf'between about 230 and v360" and a pressuregofj30-kk to,30Qp.s.i.g.,`.er'nploymg an air feed ofaboutzlO tof'5`0 y cu. -Vftpper hr.per lb. of paratlin `wax vchargaandga. superficial air velocity inVthereactor betweenr about '-0.1257-` and 1.0 feet/second. vBysuperricial velocity .o f'airu'fejedwg wev mean the quotient of theexpression (cufft. pensecond l ofair feed measured` at 60T F. andreactor inletfjprsV sure+cross section normal to air ilovvl of the emptyre-x'y n actor'in sq.A ft). .The product of air oxidationis exceedinglycomplex mixture of carboxylic acids, ketOneS, Y 'i y esters, alcohols,aldehydes, lactones, etc.r rT116Plceding airoxidationprocessfordeoiledwax is equally applicable,"v

for -paranic l1;vlbe`. oils .V r, v A

The commonm'etalliferous catalysts usedfinfgajr"r titiller@Suchpolyvalentmetalcompundsasnphthnates;` stearates, organic acidsandthe like. 'Such'componds offf manganese, chromium, vanadium, calcium,zinc, lead, titanium, mercury and cerium are useful catalysts. Forexample, in the air oxidation of paraffin wax, potassium permanganate isthe preferred catalyst and it is employed in amounts ranging from 0.1 to1% of the total wax charge, preferably about 0.4% and is dispersed inthe wax as a water solution (which distributes the perm-anganateuniformly during the air oxidation). Alternatively, oxides such asmanganese dioxide, zinc oxide and the like can be used.

SECOND STAGE-WATER EXTRACTION In the second stage of our process the airoxidized product is heated `and mixed with Water at a temperaturebetween about 100 and 500 F. preferably between 150 and 350 F. Thepressure under which this second stage extraction is conducted dependsupon the extraction temperature. The pressure must be suiiicient tomaintain the extractant water in the liquid phase. For example, forextraction temperatures of about 212 F. and below, atmospheric pressurewill suce while the temperatures on the order of 300 F. will requirepressure of about 50` p.s.i.g. The pressure in the extraction step caneither be autogenous or supplied from an outside compressed gas source.Pressures above about 1000 p.s.i.g. are generally not required. Theweight ratio of Water to air oxidation product is not critical and canbe varied over a wide range, from 0.1:1 to about 10:1 with a weightratio between about 1:1 and 4:1 preferred. In the extraction process,the oxidate-water mixture is preferably agitated for a period of about lhour. After agitation the mixture is allowed to stand until phaseseparation is essentially complete. This varies from a few minutes to afew hours depending on the extraction temperature, degree of agitation,amount and type of materials employed. The lower phase contains most ofthe water and acidic materials (which phase is designated as aquef ousphase for convenience), and the supernatent phase contains unreactedparadins, various lipophilic substances, high molecular weight estersand the like (which phase we have deemed the oily phase forconvenience). These phases can be separated by simple decantation,siphoning off, or gravity separation of one of the layers. While simplegravity separation is preferred in this step of our process, acceleratedseparation by means of a centrifuge or the like is also possible. Theoily phase is preferably recycled to the air oxidation step ashereinbefore described. Before such recycling, the oily phase can befurther extracted with water to recover additional quantities of acidicmaterial and the water solution then combined with the first obtainedaqueous phase.

THIRD STAGE-NITRIC ACID OXIDATION The iinal stage of our process is thedilute nitric acid oxidation of the water extract obtained from thepreviously described water extraction step. The nitric acid strengthshould be between about 5 and 40%, preferably between l5 and 40% basedon the total weight of HNOS and water in the reaction mixture. Withinthis range we have found, contrary to the teachings of the prior art,that the nitric acid consumption per part dibasic acid produced issubstantially lower when nitric acid of a concentration of less thanabout 40% is employed than when concentrated nitric acid is employed,eg. 70%. The temperature of the nitric acid oxidation can be maintainedbetween about 120 and 400 F., preferably between 150 and 350 F. Thereaction is operated at a pressure from about atmospheric to 800p.s.i.g. The superatmospheric pressures are required when the reactionis conducted at temperatures above the boiling point of water tomaintain a substantial portion of the water and other reactants in theliquid phase. Thorough agitation of the reaction mixture is desirable.

The nitric acid oxidation can be run batchwise or continuously,advantageously by incrementally (continuously This oily layer, which isnormally the upper layer, can

be separated by any 'of the conventional means, e.g. gravity separationand recycled to the first stage of the process. The aqueous layerprimarily comprises dibasic acids and water.

Generally we prefer to concentrate the separated aqueous layer bydistillation under reduced pressure before attempting to make theultimate recovery of dibasic acids. The aqueous layer is fractionallydistilled, preferably below about 300 mm. Hg absolute pressure andvapors comprising water and lower molecular weight monobasic acids aretaken oif as distillate. The unreacted nitric acid can also be distilledolf, e.g. as a nitric acid-water azeotrope but it is preferred to arrestconcentration when the nitric acid-water azeotropic boiling temperatureis indicated at the still head.

Alternatively, prior to concentration by distillation or vaporization,it is advantageous to extract the separated aqueous phase with a higheralkanol of 4 to 18 carbon atoms, e.g., n-butanoL Z-ethylhexanol,n-decanol and preferably, isooctanol being -used in about l to 4 volumesper volume of aqueous layer. By so doing, a major portion of the highermolecular weight dibasic acid (C6-l) are eifectively extracted from theaqueous mixture by solution in alkanol along with a small quantity ofnitric acid. The extract solution so formed can then be heated directlyto cause the reaction ofthe alkanol with the dibasic acid, producingalkyl esters 'of the dibasic acids because the small amount of nitricacid in the extract solution acts as a catalyst for the esteritication.Esters of high molecular weight dibasic acids have the greatest utilityfor use iu synthetic lubricants.

Recovery of concentrated dibasic acids can be conveniently done bycrystallizing them out of the high boiling concentrate of the aqueousphase obtained from the previously described fractional distillation.The still pot residue from such distillation is cooled to approximately0 F., although higher and lower temperatures from about 40 to about 40F. can be employed. A magma of mixed dibasic acid crystals is obtainedand filtered. The filtrate, a mixture of dibasic acids and concentratednitric acid can be recycled to the nitric acid oxidation reactor becausethe dibasic acids therein are reasonably stable toward oxidation.Alternatively, the filtrate can be concentrated by redistillation andadditional dibasic acids recovered from the resulting concentrate byrecrystallization. This procedure can be repeated as many times asdesired for the recovery of additional dibasic acid values, notover'four times being the general practice.

The mixed dibasic 'acid crystals can be purified by distillation,sublimation or treating with a variety of solvent-solid adsorbentsystems such as by rcdissolving in acetone, ethyl acetate, water orchloroform, contacting the solution with activated charcoal, silica gel,adsorptive clay or the like, separating the solid and recrystallizing.Concentrates preponderating in speciiic dibasic acids can be made bycolumn partition chromatography, eg. by placing the mixed acids in anaqueous solution or a column ofmoist silica gel and washing through withchloroform-butanol mixtures containing increasing proportions of thealcohol, the acids being selected in re agregar i talline mixtureobtained from crystallizing the aqueous bottom concentrates isapproximately `as follows:

20 to 55% succinic (C4), l0 to 30% glutaric (C5), to 25% adipic (C6), 5to 15% pimelic (C7), 5 to suberic (C8) and azelaic (C9), and theremainder of the dibasic acids being of a higher molecular Weight.

When in the oxygen gas oxidation step, i.e., the first stage of ourprocess, metalliferous catalyst has been employed, it is desirable toremove the catalyst priorto the third stage nitric acid oxidation ifincreased yield of the higher molecular weight (C6-H dibasic acid is tobe obtained. The higher molecular weight dibasic acids have theaforementioned special utility for synthetic lubricants and the like.The oxidate which has been produced by oxidation with a gas such Ias airin the presence of a polyvalent metal catalyst can be simply viltered ortreated with a cation exchangeresin such as Amberlite IR-120 (the tradename for a styrene base sulfonic acid cation exchange resin made by thesulfonation of the copolymer of styrene and divinylbenzene andmanufactured by the Rohm and Hass Co.) or Dowex 50 (the trade name of asimilar Vstyrene base sulfonic acidcation exchange resin made by the DowVChemical Co.).

Suitable cation exchanges are described, for example, in

U.S. Patent 2,736,741. Other conventional methods of separation may, ofcourse, be employed.

An `alternative aspect of your invention is the use of a specificcatalyst combination in our nitric Aacid oxidation step, i.e., the thirdstage, in order to have Vthe nitric acid oxidation favor production ofthe lower molecular weight n dibasic acids such as succinic `andglutaric acid.V We have found that between 0.05 and 3% powdered metalliccopper (i.e. a iineness 50 mesh, U.S. Standard) and between 0.05 and 3%of a vanadate selected from the group consisting of alkali metalvana'date and ammonium vanadate substantially increases the yield ofsuecinic acid. The aforementioned percent quantities o-f catalyst 1 arebased on the weight of the water soluble voxidate in the nitric acidoxidation step. The catalyst components are preferably pre-mixed beforeadding to the nitric acid reactor. Separation of the catalyst from vthefinal product can be accomplished by conventional methods, erg.y ionexchange.

Our novel process can be more fully understood by referring to thesingle iigure of the drawing, which isa flow sheet of the process. Inthe drawing, paraiiinic hydrocarbon in a liquid state is charged tofirst stage yair oxidation reactor l0 through line lll. Such ahydrocarbon can be a paraifin wax obtained by solvent dewaxing aparatiin wax distillate. it the nature of the charge hydrocarbon is suchas to require the presence of catalyst during the lirst stage oxidation,metalliferous catalyst such as an aqueous solution of potassiumpermanganate can also be `charged to reactor l0 through line'lZ. Air isintroduced-through line 13 and bubbles up through the charge. Thereaction mixture is heated rapidly to a v temperature of about 340 F.and then maintained in a control range by indirect heat transferwithsubmerged' coils of heat exchange tluid. After about l to 13 hoursdepending on particular reaction conditions and charge material, thereis obtained apar-aftinhydrocarbon'oxidate having a saponiiication numberabove 200, generally approaching 500. This oxidate is withdrawn fromreactor iu by hue l5. f

At stage the oxidate can be. sentdirectly to the water extraction vesselor optionally, if metalliferous catalyst is present and metal residueremoval is desired,f fed to vessel 16 and there filtered.Thefrnetalliferous residue is withdrawn from the system through line 18.In lieu of such filtration, it is also possible to `use sequestration,ion exchange removal, chelation or precipitation of the metalliferousresidue.v v The so treated wax yoxidate isV then passed through line 19into a second stage extraction Areactnf Ztl wherein it -is vigorouslyagitatedv with water at a temperature and pressure in the rangwesheretofore described. The water is introduced intoex-y tractor 20through line 21. The average residence vtime of the reaction mixture invessel 20 should be at least several minutes and need not be longer than2 to 3 hours depending upon the degree of extraction desired. Theextraction mixture in vessel 20 is passed through 1ine22 into gravityseparator 23 (erg. a tank) wherein a lower aqueous phase and asupernatant oily phase are formed. f The oily phase is withdrawn fromseparator 23 and can be recycled to the first oxidation vessel y10 bymeans of line 24, or to the second stage extraction vessel by means ofline 25'. The aqueous extraction phase is withdrawn from separator 23and can be sent directly to the nitricl acid oxidator 34 through line26. Alternatively, if catalyst has not been removed in the air oxidationstage and removal is desired, for reasons of product purity, the aqueousextract can'be sent to metal residue separator `2S thr ugh line 27.Separator 28 can be any conventional device for the removal of dissolvedand undissolved catalyst, eg. an ion exchange column. In addition, ifdesired, concentration of the aqueous extraction phase can beaccomplished by sending the aqueous yphase. through lines 30 or 31 toconcentrator apparatus 32, eg. comprising a kettle, distillation column,still head, condenser, 4'auxiliary line and controls.

In any case, the aqueous` extract, decatalyzed aqueous extract ordistillation residue is withdrawn through line 26, line 29 or line 33respectively` into nitric acid oxidationvessel 34. Nitric acid isfedinto vessel 34 through line 35, the concentration of the Iacid beingadjustedsoY that the final nitric acid concentration in oxidation'Vessell 34 will be between about 5 and 40% based on the ltotal weight ofHNO3 and water in the reaction mixture.V During the third stageo-fnitric'acid oxidation it is .prefenable to agitato the oxidationmixture, thel pressure and temperature in this stage being regulatedwithin lthe ranges hereinbefore described.y The average residence timeof the reactionV mixture Vin vessel 34 shouldjbeat' least 10 minutesland no longer than4 hours.` By-productV gases, eg., carbon dioxide,nitrogen, nitric oxide, 'nitro-.y sgenjdioxide and nitrous oxide arevented from line 36. Nitrous gases of nitric oxide orY nitrogen ina'highe'rstage a kettle, dstilling column, still head, condenser,auxiliary! linesand controls, Low boiling materialsY vsuch Yas water,Av

monobasic 'acids and nitric acids are withdrawn fronifthefrv stillhe'adin' a conventional manner andksentl to tankagej" through lines 39, 40and 41, respectively. The krec'vf` ered nitric acid v can be utilized inoxidation Vesself34t." Preferably, when the nitric acid-water azeotrpe(68% x HNOS- 32% H2O) boiling .temperature (249 (at 760 mm. Hg) occursduring distillation, concentration arrested yand the still lbottoms arepassed through line 42 Y Y into crystallizr 43, wherein the stillbottoms arejcooled t`o about 0 YOptionally, before cooling nitric acid`traces can be removed by treatmentof the stillbottoms with a Yweaklybasic ion exchange resin, e.g.,; the kindk iff described in U.S. Patent2,689,832. Alternatively, much .K t I orali of the nitric acid tracescan be precipitatedv witl organic bases, e.g., quinoline, orthoorrmetaitoluidine Nitron7 (the, trade name for 1,4-diphenyl-3,S-endaniloasesora-ingaande), or tirelire, and the; 'sau bottoms yliltered. Afterncooling there resultsv aslurry. ofy crystalline dibasic acids in'mother liquor. Thisfis passed through line 44 intoseparator 45, e.g., afilter. Moth liquor is withdrawn from line 46Aand can befurther.con-v 'vcentrated, recrystallizred. and v separated from .retainedfdi basic acidvalues. However, themother liquor is" prefer and sent to apparatus 38for concentration of the/dibasic L; y acid product.v Any conventionalapparatus Ymay be ernv Y ployed, e.g.`a fractional distillationapparatus compris ably recycled to vessel 34 through line 46 for nitricacid oxidation along with fresh water soluble parathnic oxidate. Mixeddibasic acids are withdrawn from separator 45 by means of line 47 andmay be further purified by distillation, sublimation orrecrystallization from solvents, optionally after having been treatedwith a solid absorbent such as activated charcoal.

A further embodiment of our process includes withdrawing at least aportion of the aqueous phase from vessel 34 through line `48 intoextractor 49. Herein a higher alkanol such as iso-octanol is admittedthrough line 50, thoroughly contacted with the aqueous material, andseparated into a rainate phase, which is withdrawn through line 51, andan extract solution phase which is withdrawn through line 52. The oilyraiiinate can be recycled to vessel 20 for further extraction. Theextraction solution which is withdrawn through line 52 and whichcontains alltanol, dibasic acids and a small portion of nitric acid canbe used directly as an esten'cation reaction mixture.

The material of construction for the air oxidation reactor is preferablyaluminum or an austenitic stainless steel but also can be made of othercorrosion resisting materials such as glass lined steel and the like.Corrosion resistant equipment Such as austenitic stainless steel ispreferred throughout. The intermittent storage facilities, pumps, valvesand other auxiliary equipment have not been shown in the foregoingdrawing but are provided wherever necessary or desirable.

The following examples show ways in which our invention has beenpracticed but are not to be construed as limiting the invention. ExampleI and Example III- Run 3 do not represent methods by which our inventionis practiced but have been included for purposes of cornparison. Allparts and percentages heretofore and hereinafter recited are based onweight except as otherwise especially noted.

Example I A petroleum oxidate was made by air blowing a semirefined 125to 127 F. melting point macrocrystalline paran wax in the presence ofpotassium permanganate catalyst. 50 parts of the oxidate having aneutralization number (Neut. No.) of 296, a saponication No. (Sap. No.)of 475, an unsaponiiable content of 5.7%, a hydroxyl No. of 5 and aniodine number of 3 were charged to a stainless steel steam heatedautoclave together with 105 parts of concentrated (70.1%) nitric acidand 350 parts of water giving a nal nitric acid concentration of 17%(based on HNO3 and H2O). Stirring was started and the autoclave washeated at between 300 and 320 F. for 2.5 hrs. during `which time thepressure rose to 510 p.s.i.g. 'I'he reactor was cooled to roomtemperature and the resultant gases were bled olf. The liquid productwas blended with 100 parts by volume of chloroform and then siphonedfrom the reactor. The aqueous and organic layers were separated bygravity separation. The aqueous layer was passed through the hydrogenform of the sulfonated copolymer of styrene and divinylbenzene cationexchange resin (Amberlite IR 120) to remove any metallic cations andsubsequently the crude dibasic acid crystals were separated from theaqueous phase by vacuum distilling ott the water and nitric acid at apressure of between 15 and 50 mm. Hg absolute emploing a boiling water(212 F.) bath. The yield of residuum dibasic acid crystals was 30.5parts equivalent to 61% of the wax oxidate charge. These crystals had aNeut. No. of 812 and by liquid liquid-partition chromatography wereshown to contain 29% succinic acid, 23% glutaric acid, 13% adipic acid,7.9% pimelic acid, 6.2% suberic and azelaic acid and 20.9% dibasic acidshaving more than 9 carbon atoms. Taking into account the :amount ofnitric acid recoverable, calculations found that the nitric acidconsumption was 2.3 parts nitric acid (as 100%) per part of dibasic acidproduced.-

The chloroform extract was stripped of chloroform by heatingthe extractsolution at 212 F. leaving a viscous dark oil having a Neut. No. of 427amounting to 4 parts which is equivalent to 8% of the original oxidatecharged.

In ord'er to show the remarkable decrease in the consumption of nitricacid in contrast to the non-water extraction process of Example I, thefollowing typical example is presented.

Example ll 500 parts of wax oxidate prepared by air blowing semirefined125 to 127 F. melting point macrocrystalline paraln wax in the presenceof potassium permanganate having a Neut. No. of 296, a Sap. No. of 475,an unsaponiable content of 5.7, a hydroxyl No. of 5 and an iodine No. of3 was charged to a stainless steel steam heated autoclave together with500 parts of water. Stirring was started and the autoclave was heated at300 F. for one hour during which time the pressure rose to 60 p.s.i.g.Subsequently, the reaction mixture was cooled and allowed to stand for 2hours to permit the separation of the aqueous and organic layer. Thelower aqueous phase was drawn ott from a dip tube which extended intothe bottom of the autoclave. The water extraction solution was found tocontain 34.1 parts by weight of water soluble oxidate per 100 parts byvolume of solution.

100 parts by volume of the aqueous extract together with 102 parts byvolume of concentrated (70.1%) nitric acid and 384 parts by volume Waterwere charged to a B-neck Pyrex flask equipped with a stirrer, droppingfunnel, thermometer and retlux condenser. The weight ratio of the watersoluble oxidate/nitric acid (100%)/water was 1/3/ 15 therebyestablishing a nitric acid concentration of 17% based on the HNO3 andwater. The reaction ask was heated at between 212-214 F. and thereaction mixture was stirred for a one hour period. A small portion ofthe reaction mixture was set aside for potentiometric titration todetermine the unconsumed nitric acid. i

The remainder of the reaction mixture was passed through an ion exchangecolumn filled with the hydrogen form of Amberlite IR-120 ion exchangeresin to remove any metallic cations and subsequently the crude dibasicacid crystals ,were removed from the aqueous phase by distilling off thewater and residual nitric acid at a reduced pressure of between 15 and50 mm. Hg absolute employing a boiling water (212 F.) bath. The yield ofdibasic acid was 88% based on the water soluble oxidate fraction. Thedibasic acid crystals had a Neut. No. of 699 `and byliquid-liquid-partition chromatography were shown to contain 26%succinic acid, 14% glutaric acid, 13% adipic acid, 8.3% pimelic acid,11.1% suberic acid and azelaic acid and 27.6% dibasic acid havinggreater than 9 carbon atoms. Taking into account the amount of nitricacid recoverable, it was found that nitric acid consumption amounted to0.6 part nitric acid (as 100%) part of dibasic acid produced.

A comparison of the nitric acid consumption values in Examples l and IIestablished that almost a reduction in nitric consumption is obtainedwhen the air oxidized wax product is extracted with water and furtheroxidized with dilute nitric acid.

While Examples I and II illustrate the remarkable saving in nitric acidwhen a water extraction step is inserted between the initial airoxidation and final nitric acid oxidation, the following exampleillustrates Vanother surprising feature of our method, namely, theemployment of very dilute nitric acid for the maximum utilization ofsaid acid.

Example III Three part by volume portions of the aqueous extractsolution phase of Example II were respectively oxidized inthe mannerdescribed in Example II with nitric acid concentrations of 17%, 40% and52% (based on VHNO3 and water). It was foundithat of these three acidconcentrations, the 17% acid gave the lowest acid consumption per partof dibasic acid recovered with nitric acid concentrations of less thanabout 40% being satisfactory. This is shown in the followingtable:

TABLE I Run 1 Run 2 Run 3 Reaction Conditions:

Aqueous extract phase, m1 100 100 100 Nltrlc Acid (70.1%) ml 102 102 102Water, m 384 39 0 Oxidation Temp. F 212-214 210-216 160-172 ReactionTime, rs 1 1 Wt. Ratio by Water Soluble Oxidate/HNOs/HrO 1/3/15 1/2/4.51/4/3.7 Nitric Acld Conc., Wt. Percent. 17 40 52 Reaction Results:

Dlbasic Acid, Neut. No 699 748 731 Dibasic Acid Yield, Wt. Percent(Based on Water Soluble Oxidate) 88 85 87 Nitric Acid Consumption (PartsHNOa Consumed/Parts Dibasic Acid Produced) 0. 6 0. 7 0.9 Analysis ofDibasic Acid Product' Succim'c 26 25 26 Glutaric- 14 13 15 dipic 13 1311 irgelic 8. 3 7. 4 8. 8

u eric Azelakh 11. 1 9. 9 9. 9 Others- 27. 6 31. 7 28.3

The following example demonstrates the applicability of our process toparaiiinic hydrocarbons other than paraffin waxes.

Example IV 1000 parts of a parainic lube Ioil oxidate, prepared by airblowing the paraiiinic lube oil of SAE 8 grade having the followingproperties:

Gravity, API 30.5-325 Flash, COC, F. 400 Viscosity, SUS:

At 100 F. 145 At 210 F. 42.7 Viscosity index 95 Pour, F. 0

autogenous pressure. Subsequently, the reaction mixture was cooled andallowed to stand overnight to effect separation `of the aqueous andorganic layers. The lower aqueous phase was dnawn ott through thestopcock. When the water was stripped off from the aqueous layer under areduced pressure of -50 mm. Hg absolute utilizing a boiling water 212F.) bath as the heat source, a dark viscous oil remained which was thewater soluble fraction of lube oil oxidate. This water soluble fractionamounted to 19.3% Vof the total lube oil oxidate and had a Neut. No. of417 and a Sap. No. of 646. The organic naiiinate layer had a Neut. No.of 14,6 and a Sap. No. of 362.

To a stainless steel steam heated autoclave, there was charged 52 partsof the above w-ater soluble extract, 74 parts of concentrated (70.1%)nitric acid and 264 parts of water which established a 15% nitric acidconcentration (based ion HNO3 and H2O). Stirling was started and thelautoclave was heated at between 300fand 305 F. for a period of one hourduring which time the pressurel rose to 500 p.s.i.g. The reactor wascooled to room temperature andthe resultant gases were bled oil? througha caustic trap. The reaction mixture was passed through an ion exchangecolumn filled with the hydrogen form of Amberlite IR-120 ion exchangeresin to remove kmetallic cations, the crude dibasic acids wereseparated from the aqueous phase by distilling ol the water and ExampleV The reaction condition ingredients and ingredient amounts wereidentical to those of Run 3 in Example III except in the third stageofthe process, i.e., the nitric acid oxidation 0.003 part of ammoniumvanadate and 0.003 part of powdered copper per part water solubleoxidate was introduced into the reaction mixture. A crude di- `basicproduct having a Neut. No. of 773 was recovered in the yield of 85%based on the water soluble ifraction of the air oxidate.. Analyses ofthe product found it to contain 37% succinic acid, 15% glutaric acid,12% adipic acid, 7.6% pirnelic acid, 6.9% vsuberic acid and azelaic acidand 21.5% dibasic acids having greater than 9 carbon atoms.

A comparison of the above product analysis with that of Run 3 in ExampleIII showed the employment of a vanadate-copper catalyst combinationincreased the yield of succinic acid by almost 50%. Succinic acid is animi portant basic ingredient in the manufacturel of many pharmaceuticalpreparations among other things.

Obviously, many modifications and variations of this invention ashereinbefore set forth may be made without departing from the spirit andscope thereof and therefore, only such limitations should be imposed asare indicated in the appended claims.

We claim: i

1. A process lfor the production of dibasic acids which comprisesoxidizing a macrocrystalline paratiin wax with V(oxygen until theresultant reaction mixture has a saponiying the aqueous and thenon-aqueous fractions of said resultant mixture )from one another,forming a reaction mixture by contacting said :aqueous fraction atapressure between about atmospheric and 800 p.s.i.g. and at atemperature between about 120 and 400 F. with nitric acid Ahaving aninitial HNOS concentration of between about 5 and 40% based on the waterand HNO3 content thereof, g and subsequently separating the dibasicacids from said reaction mixture.

2. A process in accordance with claim 1 wherein said saponitlcationnumber is from 300 yto 600.

3. A process in vaccordance with claim 1 wherein saidl mixing isconducted at a temperature between about and 500 F.

4. A process in accordance with claim y1 wherein said mixing isconducted at a pheric and 1000 p.s.i.g. v f

5. A process in accordance with claim l wherein the ratio of the waterto said paraihnic wax oxidate is from 0.1:1.to about 10:1.

6. A process in accordance with claim l wherein said separation of saidaqueous fraction from said resultant mixture is a gravity separation.

7.v A process in accordancewith claim 1 wherein-said initialconcentration of nitric acid is between 15 Vand 40% and wherein theinitial ratio of water rsoluble portion of said paraiiinic wax oxidate`to HNOS in said reaction mixi -ture is between 5:,1 andv 1:10.

8. A process in Iaccordance with claim l wherein a:

catalyst combination of copper and a vanadate` are incorporated in saidaqueous fraction, said vanadate selected from the group consisting offalkali metal vanadate and ammonium vauadate. y Y n i pressure betweenabout atmos- 9. A process in accordance with claim 11 wherein saidcopper is present in said aqueous fraction in an amount between 0.05 and3% `and wherein said vanadate is present in said aqueous fraction in anamount between 0.05 and 3% based on the water soluble portion of theparainic wax oxidate.

10. A process in accordance with claim 1 wherein a dibasic acid fractionis recovered from said nitric reaction mixture by the extraction thereofwith a higher alkanol of 4 to 18 carbon atoms.

11. A process in accordance with claim wherein said alkanol isisooctanol used in 1 to 4 volumes per volume of said aqueous fraction.

12. A process for the production of dibasic acids which comprisesoxidizing a macrocrystalline paran wax with air until the resultantreaction mixture has a saponication number between 400 and 600, therebyforming a parafnic wax oxidate, agitating said paraiiinic wax oxidatewith Water at a temperature between 150 and 350 F. and at a pressurebetween about atmospheric and 1000 p.s.i.g., said pressure suiicient tomaintain the resulting aqueous mixture in a liquid state, maintainingthe ratio of said water to said parainc wax oxidate between about 1:1and 4:1, separating by gravity said resulting aqueous mixture into anoily `fraction and an aqueous fraction, agitating said aqueous fractionwith nitric acid at a temperature between 150 and 350 F. and at apressure between about atmospheric and 800 p.s.i.g. to form a nitricacid reaction mixture, said nitric acid of an initial concentration insaid reaction mixture of between 15 and based on the weight of the Waterand 100% HNO3, and the initial weight ratio of the water soluble portionof said parainic wax oXidate to HNO3 maintained between 1:1 and 1:4,subsequently distilling off the nitric acid and water components of theresultant nitric acid reaction mixture under reduced pressure atelevated temperature to obtain a residue of dibasic acids.

References Cited in the le of this patent UNITED STATES PATENTS2,768,201 Hill Oct. 23, 1956 2,791,598 Brown et al. May 7, 19572,844,626 Kamlet July 22, 1958 2,918,487 Patterson et al Dec. 22, 1959FOREIGN PATENTS 633,354 Great Britain Dec. l2, 1949

12. A PROCESS FOR THE PRODUCTION OF DIBASIC ACIDS WHICH COMPRISESOXIDIZING A MACROCRYSTALLINE PARAFFIN WAX WITH AIR UNTIL THE RESULTANTREACTION MIXTURE HAS A SAPONIFICAION NUMBER BETWEEN 400 AND 600, THEREBYFORMING A PARAFFINIC WAX OXIDATE, AGITATING SAID PARAFFINIC WAX OXIDATEWITH WATER AT A TEMPERATURE BETWEEN 150 AND 350* F. AND AT A PRESSUREBETWEEN ABOUT ATMOSPHERIC AND 1000 P.S.I.G., SAID PRESSURE SUFFICIENT TOMAINTAIN THE RESULTING AQUEOUS MIXTURE IN A LIQUID STATE, MAINTAININGTHE RATIO OF SAID WATER TO SAID PARAFFINIC WAX OXIDATE BETWEEN ABOUT 1:1AND 4:1, SEPARATING BY GRAVITY SAID RESULTING AQUEOUS MIXTURE INTO ANOILY FRACTION WITH AN AQUEOUS FRACTION AGITATING SAID AQUEOUS FRACTIONWITH NITRIC ACID AT A TEMPERATURE BETWEEN 150 AND 350*F. AND AT APRESSURE BETWEEN ABOUT ATMOSPHERIC AND 800 P.S.I.G. TO FORM A NITRICACID REACTION MIXTURE, SAID NITRIC ACID OF AN INTITIAL CONCENTRATION INSAID REACTION MIXTURE OF BETWEEN 15 AND 40% BASED ON THE WEIGHT OF WATERAND 100% NHO3, AND THE INITIAL WEIGHT RATION OF THE WATER SOLUBLEPORTION OF SAID PARAFFINIC WAX OXIDATE TO 100% NHO3 MAINTAINED BETWEEN1:1 AND 1:4, SUBSEQUENTLY DISTILLING OFF THE NITRIC ACID AND WATERCOMPONENTS OF THE RESULTANT NITRIC ACID REACTION MIXTURE UNDER REDUCEDPRESSURE AT ELEVATED TEMPERATURE TO OBTAIN A RESIDUE OF DIBASIC ACIDS.